Jan III of Brabant (1300 – December 5, 1355, Brussels), also called Jean or John III, the Triumphant, was Duke of Brabant, Lothier, and Limburg (1312–1355). He was the son of John II, Duke of Brabant and his wife Margaret, daughter of King Edward I of England.

During his reign, Jan III became a powerful lord, alternately supporting France or England. He initially supported Edward III of England with his claim for the French crown during the first stages of the Hundred Years' War (1337-1345), betrothing his second daughter Margaret to Edward, the Black Prince. As his alliance with England unravelled, Brabant was retained as an ally by France with a treaty, signed at Saint-Quentin in 1347. His daughter Margaret was now to marry Louis of Male, Count of Flanders.

While his father Jan II protected a large number of Jews in his castle of Genappe and allowed them to establish banks; under Jan III they fared less better. The majority of Jews were victims of the 'Black Death' persecutions. In Louvain, all the Jews were delivered to the flames (1349 and 1350).

Jean III was granted the right to strike gold coins by Emperor Louis of Bavaria. In the Ordinance of 9th January 1336 Jean, agreed with Guillaume I of Holland and Hainaut to manufacture a coin that would circulate in the lands under their respective sway. To accomodate trade between Flanders and Brabant, an agreement was made with Count Louis I of Flanders to mint coins in Gent and Leuven.

After his death Jan III was buried in the Cistercian Abbey of Villers (now in Belgium). His sons having predeceased him, he was succeeded by his daughter Joanna.